A pneumatic tire is generally required to exhibit good performances in different physical properties simultaneously. Some component members of a tire such as a tread in particular are strongly requested to realize good rolling resistance properties and good wear resistance in a compatible manner in a resulting tire. However, good rolling resistance properties and good wear resistance are basically incompatible with each other. A number of trial-and-error attempts have therefore been made to make good rolling resistance properties and good wear resistance compatible.
Hydrated silica is used as a reinforcing filler in a rubber composition for a tire tread. In general, an increase in content of hydrated silica blended in a rubber composition for a tread of a tire improves wear resistance to some extent but possibly deteriorates rolling resistance properties of the tire. Further, an increase in content of hydrated silica in such a rubber composition as described above may unnecessarily enhance viscosity of unvulcanized rubber, depending on applications, thereby deteriorating workability of the rubber composition.
In view of the situation described above, there has been developed a technique of improving rolling resistance properties of a tire by using hydrated silica having large-sized primary particles in the tire to improve dispersibility of hydrated silica particles into a rubber component.
However, storage modulus and possibly wear resistance of a tire may deteriorate, although rolling resistance properties of the tire improve to some extent, in a case where hydrated silica having large-sized primary particles is used. Further, use of such hydrated silica having cohesive force thereof adjusted as described above in place of the conventional hydrated silica still has room for improvement in terms of well achieving good rolling resistance properties and good wear resistance in a satisfactorily compatible manner.
Therefore, considering that use of hydrated silica having large-sized primary particles possibly deteriorates storage modulus of the tire, a technique of using hydrated silica having a cohesive force factor and cetyltrimethylammonium bromide (CTAB) adsorption specific surface area each adequately adjusted in a rubber composition of a tire has been disclosed in order to improve storage modulus and low heat-generation property of the tire, while maintaining good dispersibility of the rubber composition (PTL 1).
Hydrated silica particles in a coagulated state of PTL 1 generally have a number of pores on the collective outer surface thereof and each pore opens at an opening portion thereof in the outer surface. These pores are involved with adsorption of rubber molecular chains. In this connection, there is a demand for optimizing a rubber-capturing volume, which closely relates to wear resistance performance, of silisic acid hydrate of PTL 1, in order to further enhance wear resistance of a tire.